1. Field of the Invention
This invention relates to a paper web threading apparatus for a rotary printing press for threading a paper web through a paper web threading path extending from a paper web supply section through a printing section to a folding section to thereby conduct printing of the paper web, and more particularly to a paper web threading apparatus for effective use in a printing press having a paper web threading path which extends from a paper web supply section through a plurality of guide rollers and turning bars including a double ender device and a bay window device to a folding section, the arrangement being made such that the threading of a paper web is conducted by a paper web guiding member adapted to be moved on and along a guide path provided along the paper web threading path.
2. Description of the Prior Art
The above-mentioned paper web threading apparatus is publicly known from the art disclosed in U.S. Pat. No. 3,127,079 (which will be referred to as "Prior Art I" hereinbelow), the art disclosed in Japanese Patent No. SHO 48-36325 (which will be referred to as "Prior Art II hereinbelow), the art disclosed in U.S. Pat. No. 3,995,553 (which will be referred to as "Prior Art III" hereinbelow), and the art disclosed in Japanese Laid-Open Patent Application No. SHO 57-1153 (which will be referred to as "Prior Art IV" hereinbelow).
These prior arts I, II, III and IV show paper web threading apparatuses each comprising a guide path provided along a paper web threading path, and a paper web guiding member adapted to be moved on and along the guide path. The prior art I provides a configuration wherein the paper web guiding member is a flat, flexible and elastic belt piece, and the belt is held or sandwiched between a plurality of pairs of pressing rollers and drive rollers provided at upper and lower positions along the guide path, the arrangement being made such that when the drive rollers are rotatively driven the belt is moved on and along the guide path. Further, the prior art II provides a configuration wherein the paper web guiding member is a guide wheel provided with a toothed drive wheel and a driver means, and the guide path is a toothed rail adapted to mesh with the toothed drive wheel, the arrangement being made such that when the toothed drive wheel is rotatively driven by the driver means the guide wheel is self-propelled on the toothed rail. Still further, the prior art III provides a configuration wherein the paper web guiding member is a chain having a predetermined length which mesh with a plurality of sprocket wheels provided along a guide path, the arrangement being made such that when the sprocket wheels are rotatively driven the above-mentioned chain is constantly moved along the guide path. Further, an air motor is used to drive the sprocket wheels, and a sensor (in particular, air sensor) is provided in the vicinity of the sprocket wheels mounted on a guide path to detect the start and stopping of the air motor and also detect the arrival of the ends of the chain. Yet further, the prior art IV provides a configuration wherein the paper web guiding member is a flexible member having a cross-sectional shape so as to provide substantially the same magnitude of resistance to flexure in every direction, such as, for example, a rope or winding having a circular or polygonal section, and the flexible member is held or sandwiched between a plurality of friction wheel groups provided at upper and lower positions along a guide path, at least one of the friction wheels in each group being used as a drive friction wheel, the arrangement being made such that when the drive friction wheels are rotatively driven the flexible member is moved on and along the guide path.
The above-mentioned prior arts have the following problems, respectively.
In the first place, the prior art I was disadvantageous in that since the paper web guiding member is a flat piece of belt, a slip tends to occur between the belt piece and the drive rollers adapted to move the belt piece along the rail thus making it difficult to guide a paper web smoothly, and intermittent guidance of the paper web which results from the slip will apply uneven tension to the paper web thus cutting the latter. Further, according to the prior art II, the paper web guiding member is a guide wheel which is provided with a drive means and which needs to be self-propelled along the rail, and therefore the whole size of the guide wheel and the rail becomes large and a large space is required for the running of the guide wheel. Therefore, the prior art II is not suitable for threading a paper web through a path including many turning points having a small radius of curvature as at turning bars or the like. Still further, according to the prior art III, the paper web guiding member is a chain, and some of the problems appendant to the above-mentioned prior arts I and II could be settled thereby. However, since the chain is allowed to flex or bend in two directions, but is not allowed to twist at all, it is impossible to thread a paper web by way of turning bars. Moreover, since the system for controlling the operation of the sprocket wheels to move the chain on the rail is complicated in construction, there is a large tendency for problems to occur such as difficulties in driving. Yet further, according to the prior art IV, the paper web guiding member is a flexible member having a cross-sectional shape so as to provide substantially the same magnitude of resistance to flexure in every direction, and problems appendant to the prior arts II and III could be solved thereby. However, since the above-mentioned flexible member has a circular or polygonal cross-sectional shape, and the area of contact between the flexible member and the friction wheel groups for moving the flexible member on the rail tends to become very small, a slip tends to occur between the flexible member and the drive friction wheels of the friction wheel groups for moving the flexible member on the rail, thus rendering it difficult to guide a paper web smoothly and bringing about the same disadvantage as that of the prior art I. In case the angle of the flexible member wound around the drive friction wheels is increased to prevent such difficulties from accurring, it becomes necessary to provide more than three friction wheels in each friction wheel group thus making the overall size of the apparatus large. Further, when threading of a paper web is conducted with a large angle kept between the drive friction wheels and the flexible member wound round it, the paper web is pulled out unavoidably in an extra amount corresponding to the large winding angle thus causing a slack in the paper web being threaded in an amount more than what is actually required. Further, the above-mentioned flexible member is allowed to flex in every direction with substantially the same resistance to flexure. When the flexible member is moved on and along the guide path in such a manner that it may flex in every direction, if the positional accuracy of the guide path is low or the guide path is deformed for some reason, there is a tendency of an ineffective tension being exerted on the paper web in other directions than those in which the paper web is allowed to flex, thus causing a tendency of the paper web being torn off by the tension.